Because the only thing better than cat videos is combination physics/cat videos. Quoth the folks at Funnycatsandnicefish:

Ninja Kittens (aka "Crouching Tiger") studied martial arts, learned how to run, climb, stalk, attack, and now began preparations for the flight to Mars! In between workouts kittens playing, studying in a ridiculous dance choir and learn to dive. And then again to study science. In this video, kittens learn physics.